Gabriele Virzi' Mariotti

Determination and analysis of the head and chest parameters by simulation of a vehicle-teenager impact

This paper reports the results of multi-body numerical simulation of a vehicle crash with a teenager pedestrian. A previous technique utilized for adult pedestrian impact is applied. The work starts with the determination of the masses for the various segments of the body of a teenager with a total mass of 45 kg and then switches to the construction of the dummy and the middle-class vehicle in the Visual Nastran environment. Simulations are performed for both frontal impacts and lateral impacts, when the vehicle is travelling at a constant speed and when the vehicle is braking, following the Euro NCAP rules on the subject. The results are analysed by calculating the values of the head injury criterion for the head and the values of the thoracic trauma index and 3 ms criterion for the chest; the injuries are assessed according to the current interpretation. Abbreviated injury scale curves are used to determine the dangerousness of the impact. Finally, the results are close to those obtained by applying the same technique to an adult pedestrian and other available data in the literature for an adult or a child.

Braking procedure analysis of a pegs-wing ventilated disk brake rotor

Fade test results of a ventilated disk brake rotor with pegs-wing performed by means of an inertia dynamometer, consisting of 14 repeated brake applications from an initial brake speed of 160 km/h down to 0 km/h, with constant deceleration are shown. The first brake application test results are compared to the FEM numerical predictions with MSC Visual Nastran on the entire disk. These conform well to the experimental data, although numerical thermal field is slightly higher than the experimental one. Besides, ventilated disk brake rotor shows great dimensional stability and the ability to dissipate a great amount of thermal flow.

Active magnetic bearing design study

The purpose of this paper is to propose a useful method to implement active magnetic bearings (AMBs) on an existing rotating shaft which rotates on conventional bearings. This is feasible if AMBs can produce the same reaction loads of conventional ones and if the size of vane is large enough to host an AMB. As this substitution could offer some difficulties due to the different size between magnetic bearings and conventional ones, a set of equations are performed to show that a variation of some parameters can solve this problem. The journal ratio is the geometrical parameter introduced to develop the present analysis. The variation of journal ratio does not produce a variation of the pole’s surface so that the reaction load does not change. The results are analyzed by numerical analysis by mathematical relationships involving the design parameters, magneto-static simulations and dynamic simulation on shaft when it is tested by disturbance rejection and reference tracking input in order to analyze the differences on dynamic behavior of the shaft on its suspended sections. Results show that the displacement pattern of the suspended sections remains unchanged, confirming that the reaction load, produced by pole expansion, remains the same varying the journal ratio.

Optimisation of a vehicle shape by CFD code

In this paper, fluid dynamics simulations have been executed using a CFD (Computational Fluid Dynamics) commercial code, on a Maserati Biturbo mod. 222 - 1988. At first some surfaces are optimised, choosing the more important ones for the reduction of the resistance, by a manual variation of their geometry, hence a large surface is optimised in an automatic way, by means of an own software, developed in the MatLab environment, returning the optimised surface according to a specific objective function (the resistance in this paper). The aerodynamics resistance results are given under the form of aerodynamics penetration coefficient CD, taking into account the vehicle shape effect, the speed, the fluid properties and the orientation.

BEM application on an external problem comparison with both theoretical and finite elements results and observations on divergence strip

Abstract By means of a computer program the Boundary Element Method is applied to a central hole in an undefined plate with uniform load along the boundary. Results are compared with those obtained by Kirschs theoretical solution and a previous analysis by the Finite Element Method. The calculus of percentage error shows the advantage of the Boundary Element Method on the external problem with regard to the Finite Element Method. The error causes near the boundary internal points are analysed with the existence of a strip, where the result is not reliable in evidence.

Design and use of a Fatigue Test Machine in Plane Bending for Composite Specimens and Bonded Joints

Polymeric and composites materials are used increasingly as structural parts in industry and therefore many informations on mechanical properties (creep, relaxation, fatigue life) are necessary. Composite materials behavior subjected to fatigue load is very complex due to non homogeneous and anisotropic properties, and it has been studied for a long time; however, composite materials design is still based on very long fatigue tests and high safety factors are used. Composites industry uses various types of resin (usually epoxy or polyester resin) and reinforced fibers (usually fiberglass). Many industrial components and consumer goods are made in this way, such as parts for boats, car components, etc. Composites with polymer matrix are used by the industries with much performed resins and stubborn and rigid reinforced fiber. Composite materials are used primarily in aerospace, military and automotive industries, however, are also utilized in sports such as golf, fishing, skiing (and snowboarding) and in the naval industry (Marannano & Virzi Mariotti 2008). These materials have very high mechanical properties such as low weight, high strength and stiffness, good formability and high design flexibility. Many theoretical studies (Van Paepegem & Degrieck, (b) 2001; Van Paepegem & Degrieck, 2002 ;Marannano & Pasta 2006; Natarajan et al. 2005) are dedicated to the study of crack propagation, applying the concepts of fracture mechanics. Fatigue failure can be described as a sequence of two phases: • crack formation; • crack propagation. The crack propagation has been studied carefully, ignoring the formation crack, and precracked specimens are used for this purpose; the study requires the development of equipping, methodologies and specialist analysis. Fatigue studies usually require several days (sometimes weeks) of load cycles to obtain an appreciable damage. The tests show inhomogeneous results, so it is necessary to do many repetitions to get a more accurate

Determination of Torsional Stresses in Shafts: From Physical Analogies to Mathematical Models

This paper presents the historical development of methods used for the study of torsional stresses in shafts. In particular, the paper covers both analog methods, especially those based on electrical analogies proposed circa 1925, and numerical methods, especially finite difference methods (FDM), finite element methods (FEM) and boundary element methods (BEM).

On the history of torsional stress concentrations in shafts: From electrical analogies to numerical methods

This article proposes a retrospective on experimental and numerical methods developed throughout the past century to solve the torsion problem in shafts, with particular emphasis on the determination of shear stress concentration factors in discontinuities of typical use in shaft design. This article, in particular, presents the theory and related solutions distinguishing between two classes of geometries: shafts with constant cross section and axisymmetric shafts with variable diameter. Emphasis is given to approaches based on physical analog methods and, in particular, those based on electrical analogies proposed since about 1925. Experimental methods based on structural physical models and numerical formulations are also reviewed, and a number of results from different approaches are collected and compared for two typical design case studies: a constant section shaft with a keyway and an axisymmetric shaft with a shouldered fillet.

Optimal Damping Constant Investigation on a Quarter-Car

This paper shows an investigation on optimal damping constant performed in the frequency domain. The optimal damping constant is meant as that value that minimizes the acceleration of all connected bodies characterizing a two degree of freedom system sketching a quarter car. The connected bodies are sprung and unsprung mass respectively for quarter of chassis and tire, this last keeps the contact with the ground and it is connected with the sprung mass through a shock absorber characterized by spring and fluid damper. Optimal damping constant was determined by imposing analytical conditions on the expression of acceleration of two masses. Afterwards, the variation of acceleration and position in function of frequency for the obtained value of damping constant is plotted numerically in two ways using Wolfram Mathematica and MSC Adams software.

Influence of Uncertainties on PD Tuning

The aim of this work is to present a method for tuning the parameters of PD controller under the influences of the uncertainties, in order to stabilize the position of a rotor supported by active magnetic bearings (AMBs). The uncertainties are relative to mass, transverse and polar moment of inertia of the rotor. The introduction of the uncertainties is due to an incomplete modeled dynamic of the system or in the case the system being subjected to a parametric variation. The presence of the uncertainties produces a set of differences among the values of the output. Poles displacement method is used to reach the asymptotically stability condition characterized by a periodic oscillation during the transient response as a consequence of the impulse input. In this way we carried out some particular condition under graphical representation which helps making a prevision when the phenomena of instability occurs. In the present approach the poles displacement is obtained by imposing respectively the condition on the real part, which must be negative, and in the discriminant of a second degree equation, which must be less than zero, both depend on the uncertainties and the angular speed of the rotor. All calculations are performed through a 4-axis AMB rigid rotor to validate the PD controller method rule introduced in this work.